Electro-thermal heating has become an effective choice for airfoil and structure deicer heaters, especially when composite materials are used for the airfoils and/or structures being deiced. An electro-thermal heater may be used wherever icing conditions exist, including applications such as: airfoil leading edges of wings, tails, propellers, and helicopter rotor blades; engine inlets; struts; guide vanes; fairings; elevators; ships; towers; wind turbine blades; and the like, for example. In electro-thermal deicing systems, heat energy is typically applied to the surface of the airfoil or structure through a metallic heating element via electrical power supplied by the aircraft or appropriate application generators.
An exemplary electro-thermal deicing apparatus is shown in the cross-sectional illustration of FIG. 1. The apparatus comprises a heater element layer of electrically conductive circuits 10 which may be configured as metal foils, wires, conductive fabrics and the like, for example, disposed in a pattern over a surface 12 of an airfoil or other structure 14. A deicing system 20 controls the voltage and current to the electrical circuits of layer 10 via a plurality of leads 16 to protect the surface 12 from accumulating ice. Generally, the heater element conductive pattern is implemented over or under the skin of the airfoil or structure, or embedded in the composite material itself.
An exemplary heater element pattern 10 is shown in the illustration of FIG. 2. Electro-thermal deicer patterns of this type have a tendency to give off a larger than desired cross-sectional radar image in response to radar illumination. This has become a particular problem when such deicer heater patterns are applied to military aircraft or other structures that may be illuminated by enemy radar systems. To protect an aircraft or structure from becoming a target, it is desired to keep the radar cross-section of the structure as small as possible. Accordingly, the metallic/conductive patterns of the circuits of heater element layer 10 render present electrothermal deicing apparatus impractical for use on structures where radar attenuation is of concern.